Cooling device for hot-rolled steel sheet and cooling method of hot-rolled steel sheet

A cooling device for a hot-rolled steel sheet that cools a top surface of a hot-rolled steel sheet conveyed on conveyor rolls after hot rolling, the cooling device comprising:

• when of a top surface of a cooling target region, a region demarcated by a cooling machine length and a full width in a width direction, or a region obtained by excluding a non-cooling region in a middle portion in the width direction from the demarcated region set as an entire cooling region, regions obtained by dividing the entire cooling region into three or more portions in the width direction set as width-divided cooling zones, and regions obtained by dividing the width-divided cooling zone into a plurality of portions in a machine length direction set as divided cooling surfaces,
• at least one cooling water nozzle that jets cooling water to each of the divided cooling surfaces to form a cooling water collision region on the top surface of the cooling target region and a switching device that switches between collision and non-collision of the cooling water jetted from the cooling water nozzle with the divided cooling surface, the cooling water nozzle and the switching device provided for each of the divided cooling surfaces;
• a temperature detecting device that measures a width-direction temperature distribution of the cooling target region;
• and
• a control device that controls operation of the switching device corresponding to each of a plurality of the divided cooling surfaces contained in the width-divided cooling zone for each of the width-divided cooling zones based on measurement results of the width-direction temperature distribution by the temperature detecting device, to thereby control cooling for the entire length of the width-divided cooling zone, and controls cooling of the entire cooling region with these controls together, wherein
• the single cooling water collision region overlaps the another cooling water collision region adjacent thereto in the width direction in the entire cooling region to form a cooling water collision region group in which the cooling water collision regions are connected in the width direction,
• each of the cooling water collision region groups does not overlap the another cooling water collision region group,
• the full width of the entire cooling region in the width direction is covered with the single cooling water collision region group or a pair of the cooling water collision region groups adjacent to each other in the machine length direction, and
• the cooling water nozzles forming the single cooling water collision region group have a jet axis inclined with respect to a vertical line to the top surface of the cooling target region when viewed in the machine length direction, and none of the cooling water nozzles forming the single cooling water collision group has the jet axis inclined in the opposite direction when viewed in the machine length direction.